1. Field of the Invention
The present invention relates to integrated circuits, and more specifically to integrated circuits that include photodiode-type semiconductor devices.
2. Description of Related Art
To produce a good photodiode is tricky. This is because it has to be sensitive to light and only the space charge region of the junction is capable of collecting the carriers generated by the light excitation, because of the electric field existing in this region. Now, a photodiode is more sensitive the larger the space charge region. This means that the doping gradient at the junction is low. However, if the doping gradient is low, the capacitance of the junction is also low. Now, the role of a photodiode is to store, in this junction capacitor, the carriers generated in the space charge region.
The solution normally used consists in increasing the doping gradient of the junction and the voltage applied to this junction. It is thus possible to obtain a wide space charge region combined with a high junction capacitance. Typically, a voltage of greater than 5 volts must be applied if the doping levels are high. However, current submicron integrated circuits do not allow high voltages to be used since in these technologies, the maximum supply voltage is less than 3.3 volts.